1. Field of the Invention
The present invention relates to an apparatus for growing thin films on a surface of a substrate. More particularly, the present invention relates to an apparatus for producing thin films on the surface of a substrate by subjecting the substrate to alternately repeated surface reactions of vapor-phase reactants.
2. Description of the Related Art
There are several methods for growing thin films on the surface of substrates. These methods include vacuum evaporation deposition, Molecular Beam Epitaxy (MBE), different variants of Chemical Vapor Deposition (CVD) (including low-pressure and organometallic CVD and plasma-enhanced CVD), and Atomic Layer Epitaxy (ALE), which was studied extensively for semiconductor deposition and electroluminescent display applications but has been more recently referred to as Atomic Layer Deposition (ALD) for the deposition of a variety of materials.
ALD is a deposition method that is based on the sequential introduction of precursor species (e.g., a first precursor and a second precursor) to a substrate, which is located within a reaction chamber. The growth mechanism relies on the adsorption of the first precursor on the active sites of the substrate. Conditions are such that no more than a monolayer forms so that the process is self-terminating or saturative. For example, the first precursor can include ligands that remain on the adsorbed species, which prevents further adsorption. Accordingly, temperatures are kept above the precursor condensation temperatures and below the precursor thermal decomposition temperatures. This initial step of adsorption is typically followed by a first purging stage wherein the excess first precursor and possible reaction byproducts are removed from the reaction chamber. The second precursor is then introduced into the reaction chamber. The first and second precursor typically react with each other. As such, the adsorbed monolayer of the first precursor reacts instantly with the introduced second precursor thereby producing the desired thin film. This reaction terminates once the adsorbed first precursor has been consumed. The excess of second precursor and possible reaction byproducts are then removed by a second purge stage. The cycle can be repeated so as to grow the film to a desired thickness. Cycles can also be more complex. For example, the cycles can include three or more reactant pulses separated by purge and/or evacuation steps.
ALD is described in Finnish patent publications 52,359 and 57,975 and in U.S. Pat. Nos. 4,058,430 and 4,389,973. Apparatuses suited to implement these methods are disclosed in U.S. Pat. No. 5,855,680, Finnish Patent No. 100,409, Material Science Report 4(7) (1989), p. 261, and Tyhjixc3x6tekniikka (Finnish publication for vacuum techniques), ISBN 951-794-422-5, pp. 253-261, which are incorporated herein by reference.
Ideally, in ALD, the reactor chamber design should not play any role in the composition, uniformity or properties of the film grown on the substrate because the reaction is surface specific. However, only a few precursors exhibit such ideal or near ideal behavior. Factors that may hinder this idealized growth mode can include: time-dependent adsorption-desorption phenomena; blocking of the primary reaction by by-products of the primary reaction (e.g., as the by-products are moved in the direction of the flow, reduced growth rate down-stream and subsequent non-uniformity may result, e.g., in TiCl4+NH3xe2x86x92TiN process); total consumption (i.e., destruction) of the second precursor in the upstream-part of the reactor chamber (e.g., decomposition of the ozone in the hot zone); and uneven adsorption/desorption of the first precursor caused by uneven flow conditions in the reaction chamber.
Plasma ALD is a type of ALD that is a potentially attractive way to deposit conducting, semiconducting or insulating films. In this method, the ALD reaction is facilitated by creating radicals. In some prior art methods, a direct capacitive plasma is ignited above the substrate (i.e., in-situ radical generation). However, this method can result in sputtering by the plasma, which may contaminate the film as sputtered materials from parts in the reaction chamber contact the substrate. Yet another disadvantage is that, when depositing conducting materials, arcing in the chamber can occur because the insulators used to isolate the RF from ground can also become coated with the deposited conducting material.
Another prior art plasma ALD method involves creating a plasma by igniting a microwave discharge remotely (see U.S. Pat. No. 5,916,365). This has the disadvantage of requiring a large distance between the substrate and the radical source, which can lead to recombination of radicals before they reach the substrate. Additionally, in this method, the distribution of radicals is typically non-uniform and the gas flow pattern in the reactor can be ill-defined.
A need therefore exists for an improved ALD apparatus and/or method that addresses at least some of the problems described above.
Accordingly, one aspect of the present invention provides a reactor that is configured to subject a substrate to alternately repeated surface reactions of vapor-phase reactants. The reactor includes a reaction chamber that defines a reaction space. A showerhead plate is disposed within the reaction space and divides the reaction space into a first part and a second part. The showerhead plate defines at least in part plurality passages that extend from the second part to the first part of the reaction chamber. The reactor further includes a first precursor source that is in communication with the first part of the reaction space and a second precursor source that is in communication with the second part of the reaction space. The substrate is positioned within the first part of the reaction space.
In one arrangement, the showerhead plate is a single integrally formed plate. In another embodiment, the reaction chamber comprises a first section and a second section that are secured to each other through mechanical forces and the showerhead plate is supported between the first and second sections of the reaction chamber by the mechanical forces. In yet another embodiment, the showerhead plate is configured to adjust in a horizontal direction the surface reactions on the substrate. In another arrangement, the showerhead plate can have a variable thickness. In yet another arrangement, the showerhead includes a shutter plate configured to be moveable with respect to the second plate, wherein the overlap between openings in each of the plates can be changed to tailor gas flow across the substrate.
Another aspect of the present invention provides a reactor that is configured to subject a substrate to alternately repeated surface reactions of vapor-phase reactants. The reactor includes a reaction chamber that defines a reaction space. The reactor further includes a first precursor source that is in communication with the reaction space. A substrate is positioned within the reaction space. The reactor further includes an inductively coupled plasma generating power apparatus that is positioned in the reaction chamber and is arranged to generate a plasma directly above the substrate.
Yet another aspect of the present invention provides a reactor that is configured to subject a substrate to alternately repeated surface reactions of vapor-phase reactants. The reactor includes reaction chamber that defines a reaction space. A substrate is positioned within the reaction chamber. A plasma generating apparatus has an upper surface and a lower surface. The plasma generating apparatus is positioned in the reaction chamber such that a plasma is generated between the upper surface of the plasma generating apparatus and an upper wall of reaction chamber. A first precursor source is in communication with the reaction space through an inlet. A flow guide is configured to direct the first precursor over the upper surface of the plasma generating apparatus, along a side of the plasma generating apparatus and to a space between the lower surface of the plasma generating apparatus and the substrate. The first precursor flows substantially in a first direction, which is substantially parallel to the substrate.
Another aspect of the present invention is a reactor configured to subject a substrate to alternately repeated surface reactions of vapor-phase reactants. The reactor includes a reaction chamber that defines a reaction space, the reaction space comprising a first section and a second section that are secured to each other through mechanical forces. A showerhead plate is disposed within the reaction space and divides the reaction space into a first part in which the substrate is positioned and a second part. The showerhead plate defines at least in a part plurality passages that extend from the second part to the first part of the reaction chamber. The showerhead plate is supported between a groove formed, at least in part, by the first and second sections of the reaction chamber. A first precursor source is in communication with the first part of the reaction space. A second precursor source is in communication with the second part of the reaction space.
Still another aspect of the present invention provides a method for atomic layer deposition including a plurality of cycles. Each cycle comprises supplying a first precursor to a reaction space in which a substrate is disposed, allowing the first precursor to be adsorbed onto a surface of the substrate so as to form a layer of adsorbed species, removing the first precursor from the reaction space, supplying a second precursor, passing, substantially intact, the second precursor through a showerhead plate extending over the substrate, the second precursor reacting with the adsorbed species, and removing the second precursor from the reaction space.
Further aspects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments.